Santa Clara County shopkeepers began collecting a half-cent transportation sales tax yesterday, even as the legality of the new levy was debated in court.

A decision on whether the challenge by anti-tax activists will go to trial or be thrown out of court is expected later this week. Supporters of the measure jubilantly predicted victory yesterday after the judge pointedly questioned opponents' arguments.

"It seems fitting that this frivolous lawsuit was heard on April Fool's Day," said Santa Clara Valley Manufacturing Group President Carl Guardino, who headed the campaign for the transportation tax. "We feel very confident that the court will make the right decision."

The new tax rate is 8.25 percent. The county has said it will place the extra tax receipts into an escrow account pending the court decision.

Appearing before Superior Court Judge Jeremy Fogel, opposing attorneys clashed over the question of whether the tax required more than a simple majority vote for passage.

Measure B, approved by 52 percent of county voters in November, was deemed a "general tax" by county officials because the $1 billion it is expected to raise over its nine-year life will be placed in the county's general fund.

Measure A, a companion measure approved by nearly 78 percent of voters, requested that all of the money raised by Measure B be spent on a specific list of transportation improvements, such as connecting the county rail system to BART's Fremont station and widening congested portions of Highway 101 and Interstate 880.

Challengers of the tax, including the Libertarian Party, the Santa Clara County Taxpayers Association and several individuals, argued yesterday that Measure B was really a "special tax," and should have required a two-thirds majority vote. Attorney Bob Rychlik argued that measures A and B are "inextricably linked," and that because backers of the tax intend to spend the proceeds only on transportation, the measure cannot be considered "general."

Judge Fogel probed Rychlik's logic, asking whether the measures would be legal had they been placed on separate ballots.

"Isn't it true that if the county wanted to spend (Measure B) money on jails or parks or mental health, that there is no legal impediment to that?" Fogel asked. "(Do) we have to look behind the literal language of the measure and consider the intent?"

Fogel said he will release a written decision "within a couple of days" on the county's request that the lawsuit be summarily dismissed.

Seventeen other California counties have adopted transportation sales taxes. The outcome of this case could determine whether they will be able to renew these taxes without obtaining a two- thirds vote.